Control of dynamic uplift on paleogeography and sediment volumes: insights from the East Shetland Platform in the Paleocene

Abstract

In several basins across the world, dynamic topography, which is created by internal mantle dynamics distinct from plate-boundary tectonics, has been shown to exert significant control on source-to-sink sediment distribution. In the Paleocene North Sea, peaks in sediment flux and transient uplift have  been previously associated with perturbations in dynamic topography created by a precursor to the modern-day Icelandic Plume. However, previous studies have had a limited understanding of the regional paleogeographic context of the area, due in part to data constraints. Here, we will investigate the Paleocene - Early Eocene paleogeographic and stratigraphic evolution of the East Shetland Platform in terms of the extent and timing of erosion versus deposition and how these can be used to reconstruct the behavior of an associated dynamic topography anomaly.The stratigraphic record of the East Shetland Platform and the adjacent Viking Graben were interpreted using >60 000 km² of 3D seismic data, revised biostratigraphic picks and c. 300 previously interpreted well-logs. This allowed the construction of multiple chronostratigraphic “Wheeler” diagrams, relative sea-level (RSL) curves and high temporal resolution paleogeographic maps. Using the resultant seismic surfaces and well data, sediment volumes and masses were calculated for multiple Cenozoic units, which were then used to constrain sediment fluxes deriving from Shetland.Multiple episodes of RSL fall and basinward offlap advance are recorded throughout the Paleocene, and from Late Thanetian to Ypresian, at least five well-preserved unconformity-bounded sequences are marked by prograding, alternating normal and forced regressive clinoforms of the Dornoch Formation. Temporal and spatial variations in the distribution of depocenters and individual subaerial unconformities indicate significant variability in patterns of shelf accommodation/erosion and fan deposition in the basinal Viking Graben. All of these are interpreted as a result of the complex interplay between laterally-uneven RSL fall, time-varied sediment entry point distribution, along-shore sediment transport/supply (evidenced by linear clinoform morphologies) and control by inherited topography/bathymetry. Most importantly, we infer a first-order control on erosion and sediment distribution promoted by the transiently and differentially uplifted topography of the ESP, as showcased by unconformities and paleogeographic maps.Preliminary results indicate that peak sediment fluxes may predate the Dornoch progradation and correspond to the deeper water Lista formation of Selandian to Early Thanetian age. This peak matches published well-based sedimentation rates for the Cenozoic North Sea and predates uplift curves reconstructed from drainage networks in Shetland and Faroe, but fits the peak modelled dynamic topography of the Icelandic Plume. However, sediment fluxes and knickpoint-derived uplift rates are both extremely sensitive to the ages assigned to individual units/surfaces and the temporal resolution of analysis, and the uncertainty related to these is sufficient to drastically change the ages or even presence of individual peaks.Ultimately, the area must have been influenced by shorter-wavelength spatial variations in uplift than what is assumed in typical models of dynamic topography, perhaps as a result of additional modulation of dynamic uplift by lithospheric structures of the North Sea or by some other mechanism that has not been resolved in current mantle imaging and modelling attempts.